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Report: Future climate could affect street trees

A new report says cities in the Central Valley — and all of inland California — should consider climate change when choosing varieties of street trees.
- photo by KRISTINA HACKER/The Journal

Kristina Hacker

Turlock Journal

Updated:
Aug. 3, 2018, 9:26 p.m.

Eighty-one
years from now, Turlock’s climate could resemble more of southeast California’s
high desert areas, according to a new report that says inland California
municipalities should consider increasing temperatures due to climate change
when planting street trees.

Many common
street trees now growing in the interior of California are unlikely to persist
in the warmer climate expected in 2099, according to research published in the
July 2018 issue of the journal Urban Forestry & Urban Greening.

"Urban
foresters in inland cities of California should begin reconsidering their
palettes of common street trees to prepare for warmer conditions expected in
2099 due to climate change," said the study’s co-author, Igor Lacan, UC Cooperative Extension environmental
horticulture advisor in the Bay Area.

"Our
research shows that some trees now lining the streets of cities like Fresno,
Stockton and Ukiah are likely to perform poorly in 2099," Lacan said.
"Those cities need to look at the conditions – and trees – now found in El
Centro, Barstow and Fresno respectively."

The City of
Turlock recently made changes to its street tree program.

In 2015, following
Governor Jerry Brown declaring a drought state of emergency, the City of
Turlock established an ad hoc
subcommittee to review the City’s street tree ordinances and policies. As
a result of Council’s ad-hoc subcommittee’s review of the City’s street tree
policies, the Parks, Recreation and Public Facilities Department requested to
adopt a revised Subdivision Street Tree Theme list and map.

Through the subcommittees review, it was found that many of
the species of trees on the original list should no longer be planted for a
variety of reasons, including not being drought tolerant, high root systems,
susceptibility to mistletoe or other diseases (often caused by drought) and
insufficient parkway strip space. This determination was confirmed by an
outside review by a local nursery owner and a landscape architect contracted
with the City, said Parks,
Recreation and Public Facilities Manager Erik Schulze.

“A few of the more popular drought resistant street trees you
will see around town include Keith Davey Chinese Pistache, Red Maple, October
Glory, Red Oak and California Sycamore,” said Schulze.

Report
authors Lacan and professor Joe McBride of UC Berkeley used space-for-time
substitution to come to their conclusions. They compared the most common street tree
species in cities representing each of the 16 California climate zones with
trees in cities that currently have climates that approximate the expected
warmer conditions in the 16 cities 80 years from now.

For example,
Eureka can expect a climate like Berkeley’s today; Fresno’s climate will
resemble the climate of El Centro today. The corresponding cities were
determined with climate predictions from Cal-Adapt, which synthesizes California climate change scenarios
to reach a consensus view of the magnitude of climatic warming.

"We
used the mid-range models," Lacan said. "It’s very reasonable to say
the warming predicted by the model we used is already ‘baked in,’ regardless of
any mitigation efforts. While we should take measures to prevent even greater
warming – mostly by reducing the use of fossil fuels – this study aims to help
adapt California urban forests to the warming that can be reasonably expected
to occur."

Lacan said
he and McBride were surprised to find that coastal cities and their warm
equivalents contain most of the same common urban tree species, while the warm
equivalents of inland cities seemed to lack most and, in some cases, all of the
common trees there today.

"It’s
really a sharp distinction," Lacan said. "Perhaps they were lucky,
but coastal cities are better positioned for the climate of 2099 than the
inland cities."